Mariusz Adamski and Filip Szymik grew up together in Poland before coming to the U.S. for college on tennis scholarships. They later shared an apartment on the Upper East Side of Manhattan.

Mr. Szymik and his longtime friend may have shared too much. The Securities and Exchange Commission Tuesday brought civil insider-trading charges against Mr. Szymik for allegedly passing along information he learned from his roommate that William Ackman's Pershing Square Capital Management LP was planning to make a negative public presentation...